The stability of the mature plant community has enormous significance for the overall maintenance and management of cities because the mature plant community requires little outside maintenance.

This is an ecological principle of the first magnitude, and one which must be comprehended before we can understand the vegetation of the city. To maintain pioneer communities, that is to say, to arrest their development at a particular stage of maturation, requires inputs of outside energy in order to change their natural development (e.g., mowing the grass of a power right-of-way). The mature plant community, on the other hand, proceeds to a stage of development where it can maintain itself. In terms of dollars, a backyard maintained as a segment of the original forest needs no maintenance, as a segment of the original forest needs no maintenance; a backyard which is a lawn must be mowed regularly. This is not only a fact of plant life, but it is a universal principle. It applies to the maintenance of human communities, animal communities, or any situation governed by ecological principles.